For a new generation broadband satellite communication

framework and channel model of low density parity check（ LDPC） coded adaptive coding and modulation-orthogonal frequency division multiplexing（ ALCOFDM） system are established. On the basis of analyzing fixed coding and modulation mode

a new adaptive coding and modulation scheme（ ACMS） selecting criterion which adopts weighted signal-to-noise-ratio（ SNR） is proposed

where each coding and modulation scheme is assigned with a certain range of average channel SNR and the SNR switching thresholds for throughput maximization of the system are derived effectively. Simulation results shows that the throughput of the system will raise along with weighted SNR comparing all weighted criterion on the condition that the bit error rate（ BER） of the system meets the requirement and when the greater the SNR obtained by weighting is

the greater the throughput of the system is

the SNR switching thresholds adopts three kinds of weighted methods

reduce more than 2 d B compared to adopting traditional criterion.